The United States had already qualified for Saturday’s final with wins in its opening two matches at the ITF invitational event, which offers no ranking points but has prize money.
Sock earlier beat Nick Kyrgios 6-2, 6-2 and Gavrilova defeated Vandeweghe 6-3, 4-6, 7-5 in singles play.
Kyrgios, who said he has some left knee soreness but expects to be ready for the Australian Open, was replaced by Ebden in the mixed doubles.
“It’s not terrible, but it’s not great,” Kyrgios said. “I just need to rest now and a couple of days without the load and I should be back to normal. A thing like this won’t take too long.”
Earlier, the Spanish pair of Lara Arruabarrena and Feliciano Lopez beat Lucie Hradecka and Adam Pavlasek of the Czech Republic 4-2, 4-1 in mixed doubles to give Spain a 2-1 win. Lopez had earlier beaten Pavlasek 7-6 (5), 6-4 while Hradecka gave the Czechs the lead with a 6-2, 6-4 win over Arruabarrena.
Switzerland, led by Roger Federer, plays France on Friday in its final round-robin match, with the winner to face the United States in the final.